While removing a file with dedup extents, we could have a great number of
delayed refs pending to process, and these refs refer to droping
a ref of the extent, which is of BTRFS_DROP_DELAYED_REF type.
But in order to prevent an extent's ref count from going down to zero when
there still are pending delayed refs, we first select those "adding a ref"
ones, which is of BTRFS_ADD_DELAYED_REF type.
So in removing case, all of our delayed refs are of BTRFS_DROP_DELAYED_REF type,
but we have to walk all the refs issued to the extent to find any
BTRFS_ADD_DELAYED_REF types and end up there is no such thing, and then start
over again to find BTRFS_DROP_DELAYED_REF.
This is really unnecessary, we can improve this by tracking how many
BTRFS_ADD_DELAYED_REF refs we have and search by the right type.
Signed-off-by: Liu Bo <bo.li.liu@xxxxxxxxxx>
---
fs/btrfs/delayed-ref.c | 10 ++++++++++
fs/btrfs/delayed-ref.h | 3 +++
fs/btrfs/extent-tree.c | 17 ++++++++++++++++-
3 files changed, 29 insertions(+), 1 deletions(-)
diff --git a/fs/btrfs/delayed-ref.c b/fs/btrfs/delayed-ref.c
index b0d5d79..9596649 100644
--- a/fs/btrfs/delayed-ref.c
+++ b/fs/btrfs/delayed-ref.c
@@ -543,6 +543,10 @@ update_existing_head_ref(struct btrfs_delayed_ref_node *existing,
* update the reference mod on the head to reflect this new operation
*/
existing->ref_mod += update->ref_mod;
+
+ WARN_ON_ONCE(update->ref_mod > 1);
+ if (update->ref_mod == 1)
+ existing_ref->add_cnt++;
}
/*
@@ -604,6 +608,12 @@ static noinline void add_delayed_ref_head(struct btrfs_fs_info *fs_info,
head_ref->must_insert_reserved = must_insert_reserved;
head_ref->is_data = is_data;
+ /* track added ref, more comments in select_delayed_ref() */
+ if (count_mod == 1)
+ head_ref->add_cnt = 1;
+ else
+ head_ref->add_cnt = 0;
+
INIT_LIST_HEAD(&head_ref->cluster);
mutex_init(&head_ref->mutex);
diff --git a/fs/btrfs/delayed-ref.h b/fs/btrfs/delayed-ref.h
index 70b962c..9377b27 100644
--- a/fs/btrfs/delayed-ref.h
+++ b/fs/btrfs/delayed-ref.h
@@ -84,6 +84,9 @@ struct btrfs_delayed_ref_head {
struct list_head cluster;
struct btrfs_delayed_extent_op *extent_op;
+
+ int add_cnt;
+
/*
* when a new extent is allocated, it is just reserved in memory
* The actual extent isn't inserted into the extent allocation tree
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index d58bef1..f5bf1a8 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -2280,6 +2280,16 @@ select_delayed_ref(struct btrfs_delayed_ref_head *head)
struct rb_node *node;
struct btrfs_delayed_ref_node *ref;
int action = BTRFS_ADD_DELAYED_REF;
+
+ /*
+ * track the count of BTRFS_ADD_DELAYED_REF,
+ * in the case that there's no BTRFS_ADD_DELAYED_REF while there're a
+ * a great number of BTRFS_DROP_DELAYED_REF,
+ * it'll waste time on searching BTRFS_ADD_DELAYED_REF, usually this
+ * happens with dedup enabled.
+ */
+ if (head->add_cnt == 0)
+ action = BTRFS_DROP_DELAYED_REF;
again:
/*
* select delayed ref of type BTRFS_ADD_DELAYED_REF first.
@@ -2294,8 +2304,11 @@ again:
rb_node);
if (ref->bytenr != head->node.bytenr)
break;
- if (ref->action == action)
+ if (ref->action == action) {
+ if (action == BTRFS_ADD_DELAYED_REF)
+ head->add_cnt--;
return ref;
+ }
node = rb_prev(node);
}
if (action == BTRFS_ADD_DELAYED_REF) {
@@ -2371,6 +2384,8 @@ static noinline int run_clustered_refs(struct btrfs_trans_handle *trans,
* there are still refs with lower seq numbers in the
* process of being added. Don't run this ref yet.
*/
+ if (ref->action == BTRFS_ADD_DELAYED_REF)
+ locked_ref->add_cnt++;
list_del_init(&locked_ref->cluster);
btrfs_delayed_ref_unlock(locked_ref);
locked_ref = NULL;
--
1.7.7
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